Chemical sensing based on plasmon resonance in carbon nanotubes

ABSTRACT

A method of forming a chemical sensor includes forming a dielectric layer on an electrode. A carbon nanotube film is deposited on the dielectric layer. The carbon nanotube film is patterned into strips.

BACKGROUND Technical Field

The present invention generally relates to chemical sensors and, moreparticularly, to chemical sensors that use plasmonic resonance innanotube structures.

Description of the Related Art

Surface plasmon resonance describes oscillations in electric charges atthe surface of a material that are coupled with an electromagneticfield. For example, surface plasmons may be used to represent electronoscillations at the interface between a metal and air. Surface plasmonresonance can be stimulated by illuminating the surface with light of anappropriate frequency, where the frequency of the light matches thenatural frequency of the surface plasmons.

Surface plasmon resonance is used for molecular detection probes. Forexample, in surface-enhanced Raman scattering, plasmonic effects enhancethe Raman signal from molecules by up to a factor of 10¹⁰, enablingsingle-molecule detection. Surface plasmon resonance-based immunoassaysalso allow for label-free detection of analytes. Such sensors areavailable for a wide variety of applications, ranging from gas sensingand explosive detection to cancer detection and glucose sensing.

However, conventional sensors based on surface plasmon resonance havetwo significant drawbacks. First, in the portion of the spectrum fromvisible light to the near infrared, such sensors have imperfect chemicalsensitivity due to many molecules being optically active in that region.Second, it can be difficult to miniaturize bulk plasmonic materials. Forexample, commonly used plasmonic metals, such as silver, will oxidizenear their surface.

SUMMARY

A method of forming a chemical sensor includes forming a dielectriclayer on an electrode. A carbon nanotube film is deposited on thedielectric layer. The carbon nanotube film is patterned into multiplestrips.

A method of forming a chemical sensor includes forming a dielectriclayer on an electrode. A carbon nanotube film is deposited on thedielectric layer using a Langmuir-Schafer process. The carbon nanotubefilm is patterned into strips. Conductive contacts are formed at ends ofeach of the strips.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a block diagram of a chemical sensor in accordance with thepresent embodiments;

FIG. 2 is a reflected spectral response from a chemical sensor inaccordance with the present embodiments;

FIG. 3 is a cross-sectional view of a step in the fabrication of achemical sensor in accordance with the present embodiments;

FIG. 4 is a cross-sectional view of a step in the fabrication of achemical sensor in accordance with the present embodiments;

FIG. 5 is a cross-sectional view of a step in the fabrication of achemical sensor in accordance with the present embodiments;

FIG. 6 is a cross-sectional view of a step in the fabrication of achemical sensor in accordance with the present embodiments;

FIG. 7 is a block diagram of an alternative embodiment of a chemicalsensor in accordance with the present embodiments;

FIG. 8 is a cross-sectional view of a step in the fabrication of analternative embodiment of a chemical sensor in accordance with thepresent embodiments;

FIG. 9 is a block/flow diagram of a method of chemical detection inaccordance with the present embodiments;

FIG. 10 is a block/flow diagram of a method of chemical detection inaccordance with the present embodiments;

FIG. 11 is a block diagram of a chemical sensing system in accordancewith the present embodiments; and

FIG. 12 is a block diagram of a processing system in accordance with thepresent embodiments.

DETAILED DESCRIPTION

Embodiments of the present invention provide surface plasmon resonancesensors that use carbon nanotubes to provide a surface interface. Carbonnanotubes provide resonances in the spectral range from mid-infrared toterahertz; can be tuned by chemical doping, electrostatic gating, or bytuning their length; provide a high degree of optical confinement;provide molecular specificity without surface functionalization; and canbe electrically integrated into photothermoelectric chemical sensors.

Referring now to FIG. 1, a sensor system 100 is shown. A surface plasmonresonance test surface 102 is illuminated by a light source 104.Reflected light is collected at a detector 106 and analyzed by signalanalyzer 108. It is specifically contemplated that the light source maybe a broadband source such as, e.g., an incandescent bulb, but it shouldbe understood that other light sources, such as light emitting diodes,lasers, and fluorescents, may be used instead.

The surface plasmon resonance test surface 102 of the presentembodiments uses a low-dimensional material. Although it is specificallycontemplated that carbon nanotubes may be used, it should be understoodthat other low-dimensional materials (i.e., materials that exhibit one-or two-dimensional plasmon resonances) may be used instead. In addition,materials other than carbon may be used, including for example inorganicnanotube materials.

The plasmonic resonances of low-dimensional materials, such as grapheneand carbon nanotubes, have low resonance frequencies relative toconventional bulk materials. These resonance frequencies, which can betuned by doping and/or patterning, overlap the vibration energies ofmolecules and biomolecules. When the vibrational and plasmon modesoverlap, the absorption from the vibrational mode will be plasmonicallyenhanced. The presence of molecules of interest can then be sensitivelydetected by analyzing changes in surface plasmon resonance absorption.In the far infrared and terahertz regimes, the vibrational modes ofmolecules can form a unique fingerprint, with a one-to-onecorrespondence between the vibrational spectrum and a specific module.This fingerprint allows the nanotube-based sensor to be chemicallyspecific.

The surface plasmon resonance test surface 102 is therefore exposed to asubstance or environment under test. When a molecule of interestinteracts with the test surface 102, the reflected light absorbed by thedetector 106 changes according to the fingerprint, and the signalanalyzer 108 detects the signature. The analysis performed by the signalanalyzer 108 may include, for example, Fourier transform infraredspectroscopy.

The low-dimensional geometry of graphene and carbon nanotubes alsoconfines the plasmonic modes better than bulk materials. When aplasmonic structure is miniaturized, additional spatial confinement ofthe plasmonic mode can be achieved and, in turn, a higher Purcellenhancement factor P can be provided, which characterizes the plasmonicenhancement to fluorescence. For example, the Purcell enhancement of amolecule coupled to an ideal plasmonic cylinder having a radius R willscale as ˜1/R. Miniaturizing the plasmonic materials furthermore makesthe materials closer to the size scale of the molecules to be detected,opening up opportunities for surface plasmon resonance labels to beattached to functional molecules.

The use of carbon nanotubes in particular provides the ability tofunctionalize the nanotubes in solution, such that they willpreferentially bind to certain analytes. In addition, semiconductingnanotubes have a higher photothermoelectric coefficient than does, e.g.,graphene, providing electrically integrated plasmonic sensors that havesuperior sensitivity.

Referring now to FIG. 2, an exemplary spectral curve is shown fordetection using a carbon nanotube surface plasmon resonance test surface102. The vertical axis shows a magnitude of absorption of light (i.e., adecrease in light that is detected at the detector 106 compared to abaseline) measured as a percentage. The horizontal axis shows thewavenumber of the light in inverse centimeters—wavenumber essentiallybeing a measurement of the number of wave cycles present per unitlength. A relatively broad peak is centered around 1,800/cm and has awidth of roughly 700/cm. This broad peak represents the plasmonicresonance of the nanotubes. There is a sharp peak within the broad peakthat is centered at about 1600/cm, which indicates a vibrational C—Cmode. The C—C mode is the Elu infrared-active mode of a nanotube.

Referring now to FIG. 3, a cross-sectional view of a step in thefabrication of a surface plasmon resonance test surface 102 is shown. Agate electrode 304 is formed on a semiconductor substrate 302. Adielectric layer 306 is formed over the gate electrode 304 and may beformed from any appropriate insulating material such as, e.g., silicondioxide. In one specific embodiment, the dielectric layer 306 is formedwith about 10 nm of silicon dioxide and between about 0 nm and about 40nm of diamond-like carbon on top. The diamond-like carbon provides anon-polar spacer that controls the coupling between plasmons in thenanotubes and polar photons in the silicon dioxide. A carbon nanotubefilm 308 is then formed on the dielectric layer 306.

The gate electrode 304 is used to tune the resonance of the finaldevice. In particular, applying a voltage to the gate electrode 304electrostatically modifies the charge density in the nanotubes. In turn,this charge density affects the plasmon resonance frequency and, thus,also affects the frequency of light that is absorbed when a chemical tobe detected is present.

The semiconductor substrate 302 may be a bulk-semiconductor substrate.In one example, the bulk-semiconductor substrate may be asilicon-containing material. Illustrative examples of silicon-containingmaterials suitable for the bulk-semiconductor substrate include, but arenot limited to, silicon, silicon germanium, silicon germanium carbide,silicon carbide, polysilicon, epitaxial silicon, amorphous silicon, andmulti-layers thereof. Although silicon is the predominantly usedsemiconductor material in wafer fabrication, alternative semiconductormaterials can be employed, such as, but not limited to, germanium,gallium arsenide, gallium nitride, cadmium telluride and zinc selenide.Although not depicted herein, the semiconductor substrate 302 may alsobe a semiconductor on insulator (SOI) substrate, for example with aburied oxide layer underling a semiconductor layer.

The carbon nanotube layer 308 may be deposited using, e.g., theLangmuir-Schaefer process, although any other appropriate growth ordeposition process may be used instead to produce a uniform, denselydistributed film of carbon nanotubes. This process creates a film ofnanotubes that may be between about 2 and about 10 monolayers thick. Itis specifically contemplated that the carbon nanotube layer 308 may havea thickness of about 6 nm and may be formed from about 99.9%semiconducting nanotubes. It should be noted that the carbon nanotubesbeing aligned and roughly parallel with another increases the sharpnessof the resonance signal, and improves the sensitivity of the sensor, butsome embodiments may include non-aligned nanotubes.

Referring now to FIG. 4, a cross-sectional view of a step in thefabrication of a surface plasmon resonance test surface 102 is shown. Amask 402 is formed by depositing a layer of, e.g., poly methylmethacrylate (PMMA) onto the nanotube layer 308. The mask 402 may beformed by, e.g., spinning the PMMA onto the surface and allowing thematerial to solidify, followed by etching a pattern into the PMMAmaterial. Electron-beam lithography may be used to pattern stripes intothe PMMA material, but it should be understood that any appropriateanisotropic etch process may be used instead so long as it does notdamage the underlying nanotube layer 308. While a striped pattern isspecifically contemplated for the mask 402, it should be understood thatany other appropriate pattern, for example including non-linear patternsand linear patterns having varying thicknesses may, be used instead.

In one specific embodiment, the mask 402 leaves gaps having a width ofbetween about 50 nm and about 500 nm. These gaps are oriented transverseto an orientation of the nanotubes in the nanotube layer 308, such thatthe nanotubes in the nanotube layer 308 have lengths roughly the same asthe widths of the gaps.

Referring now to FIG. 5, a cross-sectional view of a step in thefabrication of a surface plasmon resonance test surface 102 is shown.The exposed portions of the nanotube layer 302 are etched away, leavingonly nanotube strips 502 protected underneath the mask 402. The etch maybe performed using an O₂-based reactive ion etch (RIE) or any otherappropriate anisotropic etch.

RIE is a form of plasma etching in which during etching the surface tobe etched is placed on a radio-frequency powered electrode. Moreover,during RIE the surface to be etched takes on a potential thataccelerates the etching species extracted from plasma toward thesurface, in which the chemical etching reaction is taking place in thedirection normal to the surface. Other examples of anisotropic etchingthat can be used at this point of the present invention include ion beametching, plasma etching or laser ablation.

Referring now to FIG. 6, a cross-sectional view of a step in thefabrication of a surface plasmon resonance test surface 102 is shown.The mask 402 is removed using any appropriate selective etch, forexample a wet or dry chemical etch such as acetone, that selectivelyremoves the mask material without harming the underling nanotube strips502. In addition, the nanotube strips 502 may be doped. In one specificembodiment, the nanotube strips 502 are doped to p-type via exposure toNO₂ gas at, e.g., 25° C. under a pressure of about 300 mTorr for about 5minutes, although it should be understood that other forms of doping maybe used instead. Doping the nanotube strips 502 provides tuning in thefrequency tuning of the sensor. At this stage, electrical connectionsmay be formed to the gate electrode layer 304 in any appropriate mannerand the finished device may be exposed to a chemical or environment tosense particular chemicals.

Referring now to FIG. 7, an alternative embodiment of a sensor system700 is shown. In this embodiment, the surface plasmon resonance testsurface 702 has conductive terminals at the ends of its nanotube strips.A photothermoelectric detector 704 measures photothermoelectric currentsgenerated in the nanotube strips when illuminated by a narrowband lightsource 703, with an output frequency tuned to the molecular vibration ofinterest. The photothermoelectric currents represent the spectralresonance response of the test surface 702 and are provided to thesignal analyzer 108 for analysis and comparison to one or more chemicalspectrum fingerprints.

In this embodiment, narrowband light source 703 is tuned to the expectedvibrational resonance of the chemical being detected. Because detectionis performed using the photothermoelectric current, no spectral analysisis performed. The degree of absorption, and hence the magnitude of thecurrent, is modulated by the presence and quantity of the chemical to bedetected.

Referring now to FIG. 8, additional detail on the surface plasmonresonance test surface 702 is shown. In this embodiment, conductivecontacts 802 are formed at the ends of the nanotube strips 502. It isspecifically contemplated that the conductive contacts 802 may be metalor metallic electrodes, for example formed from any appropriate materialsuch as tungsten, nickel, titanium, molybdenum, tantalum, copper,platinum, silver, gold, ruthenium, iridium, rhenium, rhodium, silicides,germanicides, or any other appropriately conductive material or mixtureof materials.

The conductive contacts form electrical connections to thephotothermoelectric detector 704. When light from the narrowband lightsource 703 strikes the surface plasmon resonance test circuit 702 in thepresence of the chemical in question, the nanotube strips 502 absorb thelight and drive a photothermoelectric current between the conductivecontacts 802, thereby providing the detection signal. When the moleculein question is present, the absorption spectrum of the nanotube strips502 is modified, resulting in a modification of the photothermoelectricsignal.

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Referring now to FIG. 9, a method of molecular detection is shown. Block902 illuminates a surface plasmon resonance test surface 102 withbroadband input light from, e.g., a light source 104. Block 904 measuresthe light reflected from the test surface 102, which provides a spectralresponse based on the absorption characteristics of the nanotube strips502 in the test surface 102. Block 906 analyzes the spectral response todetermine whether the spectral response matches a spectral fingerprintof one or more molecules. If block 906 finds a match, block 908determines that the corresponding molecule is present at the testsurface 102.

Referring now to FIG. 10, an alternative method of molecular detectionis shown. Block 1002 illuminates a surface plasmon resonance testsurface 702 with narrowband light from, e.g., a light source 703. Block1004 measures a photothermoelectric signal generated by the test surface702, which provides a spectral response based on the absorptioncharacteristics of the nanotube strips 502 in the test surface 702.Block 1006 compares the photothermoelectric signal to the threshold. Ifthe photothermoelectric signal is greater than a threshold, block 1008indicates that the corresponding molecule is present at the test surface702. If not, block 1008 indicates that the molecule is not present. Insome embodiments, block 1008 may indicate an amount of the molecule thatis present based on the magnitude of the photothermoelectric signal.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Referring now to FIG. 11, a chemical sensing system 1100 is shown. It isspecifically contemplated that the chemical sensing system includes thedetection and analysis components of FIGS. 1 and/or 7, but it should beunderstood that the chemical sensing system 1100 may further include thetest surfaces and light sources. The chemical sensing system 1100includes a hardware processor 1102 and memory 1104. A detector 1106receives a signal form a surface plasmon resonance test surface 102 or702. Depending on the embodiment, the detector 1106 may be a lightsensor that receives reflected light from test surface 102 or,alternatively, the detector 1106 may be a photothermoelectric detectorthat measures photothermoelectric currents generated by a test surface702.

The chemical sensing system 1100 may furthermore include one or morefunctional modules that are implemented as, e.g., software that isstored in memory 1104 and executed by hardware processor 1102.Alternatively, the functional module(s) may be implemented as one ormore discrete hardware components in the form of, e.g., applicationspecific integrated chips or field programmable gate arrays.

In particular, the chemical sensing system 1100 may include a matchingmodule 1110 that compares the signal received by the detector 1106 toone or more chemical or molecular fingerprints in a chemical fingerprintdatabase 1108 that is stored in memory. Based on this comparison, thematching module 1110 determines a difference between the received signaland the fingerprint of a molecule in question or with all of thefingerprints in the database 1108. If the difference is within athreshold, the matching module 1110 determines that the molecule orchemical has been detected.

Referring now to FIG. 12, an exemplary processing system 1200 is shownwhich may represent the transmitting device 100 or the receiving device120. The processing system 1200 includes at least one processor (CPU)1204 operatively coupled to other components via a system bus 1202. Acache 1206, a Read Only Memory (ROM) 1208, a Random Access Memory (RAM)1210, an input/output (I/O) adapter 1220, a sound adapter 1230, anetwork adapter 1240, a user interface adapter 1250, and a displayadapter 1260, are operatively coupled to the system bus 1202.

A first storage device 1222 and a second storage device 1224 areoperatively coupled to system bus 1202 by the I/O adapter 1220. Thestorage devices 1222 and 1224 can be any of a disk storage device (e.g.,a magnetic or optical disk storage device), a solid state magneticdevice, and so forth. The storage devices 1222 and 1224 can be the sametype of storage device or different types of storage devices.

A speaker 1232 is operatively coupled to system bus 1202 by the soundadapter 1230. A transceiver 1242 is operatively coupled to system bus1202 by network adapter 1240. A display device 1262 is operativelycoupled to system bus 1202 by display adapter 1260.

A first user input device 1252, a second user input device 1254, and athird user input device 1256 are operatively coupled to system bus 1202by user interface adapter 1250. The user input devices 1252, 1254, and1256 can be any of a keyboard, a mouse, a keypad, an image capturedevice, a motion sensing device, a microphone, a device incorporatingthe functionality of at least two of the preceding devices, and soforth. Of course, other types of input devices can also be used, whilemaintaining the spirit of the present principles. The user input devices1252, 1254, and 1256 can be the same type of user input device ordifferent types of user input devices. The user input devices 1252,1254, and 1256 are used to input and output information to and fromsystem 1200.

Of course, the processing system 1200 may also include other elements(not shown), as readily contemplated by one of skill in the art, as wellas omit certain elements. For example, various other input devicesand/or output devices can be included in processing system 1200,depending upon the particular implementation of the same, as readilyunderstood by one of ordinary skill in the art. For example, varioustypes of wireless and/or wired input and/or output devices can be used.Moreover, additional processors, controllers, memories, and so forth, invarious configurations can also be utilized as readily appreciated byone of ordinary skill in the art. These and other variations of theprocessing system 1200 are readily contemplated by one of ordinary skillin the art given the teachings of the present principles providedherein.

Having described preferred embodiments of chemical sensing based onplasmon resonance in carbon nanotubes (which are intended to beillustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments disclosed which are within the scopeof the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming a chemical sensor,comprising: forming a dielectric layer on an electrode; depositing acarbon nanotube film on the dielectric layer; and patterning the carbonnanotube film into a plurality of strips.
 2. The method of claim 1,wherein depositing the carbon nanotube film on the dielectric layercomprises depositing the carbon nanotube using a Langmuir-Schaferprocess.
 3. The method of claim 2, wherein depositing the carbonnanotube film comprises forming a film of nanotubes having a thicknessbetween about 2 nm and about 10 nm.
 4. The method of claim 3, whereindepositing the carbon nanotube film comprises forming a film ofnanotubes having a thickness of about 6 nm.
 5. The method of claim 2,wherein depositing the carbon nanotube film comprises forming a film ofnanotubes of about 99.9% pure semiconducting nanotubes.
 6. The method ofclaim 1, wherein patterning the carbon nanotube film comprises forming amask on the carbon nanotube film and etching portions of the carbonnanotube film that are not covered by the mask.
 7. The method of claim6, wherein etching comprises an oxygen reactive ion etch process.
 8. Themethod of claim 1, further comprising forming conductive contacts atends of each of the plurality of strips.
 9. The method of claim 8,further comprising connecting the conductive contacts to a signalanalyzer configured to detect currents generated by the respectivestrips.
 10. The method of claim 1, wherein patterning the carbonnanotube film comprises forming gaps between the plurality of strips ofcarbon nanotubes, the gaps having a width between 50 nm and 500 nm. 11.The method of claim 10, wherein patterning the carbon nanotube filmforms the plurality of strips with about the same width as the gaps. 12.A method of forming a chemical sensor, comprising: forming a dielectriclayer on an electrode; depositing a carbon nanotube film on thedielectric layer using a Langmuir-Schafer process; patterning the carbonnanotube film into a plurality of strips; and forming conductivecontacts at ends of each of the plurality of strips.
 13. The method ofclaim 12, wherein depositing the carbon nanotube film comprises forminga film of nanotubes having a thickness between about 2 nm and about 10nm.
 14. The method of claim 13, wherein depositing the carbon nanotubefilm comprises forming a film of nanotubes having a thickness of about 6nm.
 15. The method of claim 12, wherein depositing the carbon nanotubefilm comprises forming a film of nanotubes of about 99.9% puresemiconducting nanotubes.
 16. The method of claim 12, wherein patterningthe carbon nanotube film comprises forming a mask on the carbon nanotubefilm and etching portions of the carbon nanotube film that are notcovered by the mask.
 17. The method of claim 16, wherein etchingcomprises an oxygen reactive ion etch process.
 18. The method of claim12, further comprising connecting the conductive contacts to a signalanalyzer configured to detect currents generated by the respectivestrips.
 19. The method of claim 12, wherein patterning the carbonnanotube film comprises forming gaps between the plurality of strips ofcarbon nanotubes, the gaps having a width between 50 nm and 500 nm. 20.The method of claim 19, wherein patterning the carbon nanotube filmforms the plurality of strips with about the same width as the gaps.